linux-kernel - Re: [cocci] [RFC] Increasing usage of direct pointer assignments from memcpy() calls with SmPL?

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Message-ID: <60f881dc-979d-486b-95be-6b31e85d4041@web.de>
Date: Thu, 30 Oct 2025 13:26:18 +0100
From: Markus Elfring <Markus.Elfring@....de>
To: Julia Lawall <julia.lawall@...ia.fr>, cocci@...ia.fr
Cc: LKML <linux-kernel@...r.kernel.org>, kernel-janitors@...r.kernel.org,
 Miaoqian Lin <linmq006@...il.com>
Subject: Re: [cocci] [RFC] Increasing usage of direct pointer assignments from
 memcpy() calls with SmPL?

> If you have a concern, you have to say what it is.  It doesn't seem it is
> about the running time, so why do you include that information?

How will remaining open issues be resolved?


> I should not have to repeat your experiment

It would be nice if further software users would occasionally reproduce
presented data processing possibilities.


>                                             to figure out what you are
> asking about.

I “accidentally” tried also the following SmPL script variants out.

A)
@replacement3@
expression object, size, source, target;
@@
 target =
-object; memcpy(target, source, size)
+object; memcpy(object, source, size)
 ;

Markus_Elfring@...ne:…/Projekte/Linux/next-analyses> time /usr/bin/spatch --max-width 100 --no-loops …/Projekte/Coccinelle/janitor/use_memcpy_assignment3.cocci arch/arm64/kvm/arm.c
…
@@ -2600,8 +2600,8 @@ static int __init init_hyp_mode(void)
                        goto out_err;
                }
 
-               page_addr = page_address(page);
-               memcpy(page_addr, CHOOSE_NVHE_SYM(__per_cpu_start), nvhe_percpu_size());
+               page_addr =memcpy(page_address(page), CHOOSE_NVHE_SYM(__per_cpu_start),
+                                 nvhe_percpu_size());page_address(page);
                kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu] = (unsigned long)page_addr;
        }
 

real    0m0,578s
user    0m0,524s
sys     0m0,047s



B)
@replacement4@
expression object, size, source, target;
@@
-target = object; memcpy(target, source, size)
+target = object; memcpy(object, source, size)
 ;

Markus_Elfring@...ne:…/Projekte/Linux/next-analyses> time /usr/bin/spatch --max-width 100 --no-loops …/Projekte/Coccinelle/janitor/use_memcpy_assignment4.cocci arch/arm64/kvm/arm.c
…
@@ -2600,8 +2600,8 @@ static int __init init_hyp_mode(void)
                        goto out_err;
                }
 
+               memcpy(page_address(page), CHOOSE_NVHE_SYM(__per_cpu_start), nvhe_percpu_size());
                page_addr = page_address(page);
-               memcpy(page_addr, CHOOSE_NVHE_SYM(__per_cpu_start), nvhe_percpu_size());
                kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu] = (unsigned long)page_addr;
        }
 

real    0m0,565s
user    0m0,533s
sys     0m0,032s



Would you like to reconsider implementation details accordingly?

Regards,
Markus